Sexual reproduction provides a unique opportunity for pairwise interactions between genotypes of mating pairs. When male x female interactions are involved, evolution may fail to optimize functions for either sex, and retains a high level of variation. This appears to be the case for factors influencing sperm competition and other reproductive fitness attributes in Drosophila. The accessory gland proteins (Acps) mediate aspects of these interactions, and along with the female molecules that interact with Acps, they will provide a molecular path to quantifying specific male x female interactions. Drosophila sperm competition provides a unique system for studying male x female interactions in sexaul reproduction. The first aim is to use genetic isolates from natural populations to quantify male x female interactions in components of sperm competition and ultimately, reproductive fitness with a focus on those likely to be mediated by Acps and the processes that interact in females. Paternity success in doubly mated females, fecundity, fertility, and female receptivity will be scored. This study will quantify reproductive fitness components for validation of the findings of Aim 2. The second aim is to dissect male x female interactions by testing RNAi knockdowns of specific male Acp genes across a range of well-characterized wild female genotypes. Comparisons of reproductive phenotypes will be made between control males and males with specific Acps knocked down by RNAi. Focus will be Acps that effect sperm storage or sperm competition. Female lines that are hyper- and hypo-responsive to each knockdown will be identified, and interactions will be partitioned into components mediated by each Acp. Aim 2 will identify specific interactions of Acps with female backgrounds and female response genes with male backgrounds. This will extend the understanding of the genetic variation in male and female contributions to reproduction, as well as how and why genetic variation is maintained in nature. Since the genes to be examined involve basic reproductive functions, these results will expand the foundation for understanding cases of idiopathic human infertility, specifically those in which no sex-specific cause can be identified and may reflect genetic incompatibility between the partners. PUBLIC HEALTH RELEVANCE: Drosophila melanogaster will be used as a model to quantify the male x female genetic interactions in aspects of fertility. The project aims to understand cases of aberrant fertility of particular genotype-pairs in crosses, when neither genotype by itself is unusual in its fertility. It will also be relevant to explaining the basis for human infertilities that arise from a reproductive incompatibility between the particular pair of individuals involved.